Lithium electrochemical cells and batteries are being widely exploited as power sources for numerous applications because of their high energy and power density, for example, in consumer electronics such as laptop computers and cellular phones, in medical devices such as cardiac pacemakers and defibrillators and in electric and hybrid electric vehicles.
Silver vanadium oxides, particularly Ag2V4O11, are well known as positive electrode materials for primary lithium cells for powering cardiac defibrillators in the medical industry. For example, U.S. Pat. Nos. 4,310,609 and 4,391,729 discloses the use of an electrochemical cell having as its positive electrode a composite oxide matrix consisting of a vanadium oxide chemically reacted with a group IB, IIB, IIIB, IVB, VB, VIB, VIIB and VIII metal, and most specifically with a silver containing compound. U.S. Pat. No. 4,391,729 also discloses a method of making such a cathode. In addition, several scientific papers describing the structural and electrochemical properties of Ag2V4O11 and Ag2V4O11−x and AgV3O8 have appeared in the literature, such as that of Takeuchi et al (Journal of Power Sources, Volume 21, page 133 (1987); Leising et al (Chemistry of Materials, Volume 5, page 738 (1993)); Leising et al (Chemistry of Materials, Volume 6, page 489 (1994)); Garcia-Alvarado et al (Solid State Ionics, Volume 73, page 247 (1994)); Kawakita et al (Solid State Ionics, Volume 99, page 71 (1997)); Rozier et al, (Journal of Solid State Chemistry, Volume 134, page 294 (1997)). Moreover, lithium vanadium oxide electrodes, such as Li1.2V3O8, are also well known for their good electrochemical properties in rechargeable or secondary lithium cells. For example, U.S. Pat. No. 5,039,582 discloses the use of an amorphous form of LiV3O8 as a positive electrode in a lithium cell, and U.S. Pat. No. 5,336,572 discloses the use of MxV3O8 positive electrodes for lithium cells, where M is a monovalent or multivalent metal cation. In addition, numerous research papers on the structural and electrochemical properties of LixV3O8 materials have been written, such as that of Wadsley et al (Acta Crystallographica, Volume 10, page 261 (1957)); de Picciotto et al (Solid State Ionics, Volume 62, page 297 (1993); Panera et al (Journal of the Electrochemical Society, Volume 130, page 1225 (1983)); West et al (Journal of the Electrochemical Society, Volume 143, page 820 (1996)). Spahr et al has disclosed the use of NaV3O8 as a cathode in a lithium cell (Journal of the Electrochemical Society, Volume 145, page 421 (1998)).
A problem that is encountered with state-of-the-art Ag2V4O11 cathodes in lithium cells is the deterioration of electrochemical performance, particularly the ability of the cells to deliver acceptable pulse power before the cell has reached the end of its expected calendar and operating life. It can therefore be readily understood that such limitations of Li/Ag2V4O11 cells are of great concern when used to power cardiac defibrillators in the human body. Such limitations negatively affect product reliability and necessitate a continual monitoring of the cells while implanted in patients to ensure a timely replacement of the cells before they prematurely reach the end of discharge. There is therefore a great need to improve the electrochemical properties and operating life of silver-vanadium-oxide electrodes for lithium cells and batteries, particularly for use in life-supporting medical devices, such as cardiac defibrillators.